Don't assume that - Like May/June, September/October on the west can often offer better and more stable weather than over high summer. Plus, by October, the trees in areas like Argyll and parts of Highland Perthshire will be on the turn, so glorious autumn colour. The changes also happen further north but get more subtle as the tree cover thins out.And it will be pissing down anywhere near mountains. You really should have done this in August.
Pitlochry is another good base for Perthshire/Central Highlands and over into Angus - but starting this year and through to the mid 2020s (or 2050s if your believe the Sunday Post!), there are several stretches of ongoing major improvement/rebuilding work along the A9, between Perth and Aviemore, so expect delays as they are using the 10mph one way "convoy" system to lead traffic through the roadworks. So if headed anywhere up the A9, consider turning-off at Perth and following the "Snow Roads" scenic route from Blairgowrie to Grantown on Spey instead.
The SnowRoads Scenic Route - 90 Miles of Adventure
After Grantown, its a short hop back to the A9 and IIRC, only one stretch of roadworks north of Aviemore. Or you could take the high open hill road over Dava Moor to pick-up the A96 to the back road through Cawdor and Culloden - which again is magnificent with great views to the central massif of the Cairngorms and attractive little places like Dulsie Bridge and its walk along the Findhorn Gorge (unsigned path from the back of the car park).